Secretion post-translational

Yeast. The advantages of expression in yeast include potentially high level production of proteins, the abiUty to have expressed proteins secreted into the media for ease of purification, and relatively low cost, easy scale-up. A disadvantage is that plasmid instabiUty may be a problem which can lead to low product yield. Whereas post-translational modification occurs in yeast, proteins are quite often hyperglycosylated. This is generally a problem with expression in Saccharomyces cerevisiae but not for the more recently used yeast host Pichiapastoris (25) (see Yeasts). 

Saccharomyces cerevisiae Good secretion machinery Post-translational modifications Easy scale-up Selection procedure required Tendency to overglycosylation Thick cell wall complicates purification... 

Protein processing in the endoplasmic reticulum makes mistakes. All membrane-associated proteins and proteins that are secreted by the cell are synthesised on membrane-bound ribosomes and pass into the lumen of the reticulum, where they are modified by post-translational processes, so that much biochemical manipulation of the proteins takes place. Consequentially mistakes are often made. Such abnormal proteins are exported from the lumen into the cytosol for ubiquitination and degradation in the proteasome. 

Fungi Insect cells Economical, fast, easy, high yield, well characterized genetics (yeast), glycosylation possible, able to secrete correctly folded and processed proteins Glycosylation and other post-translational modifications are often different to mammalian systems... 

Many proteins on the surface of the plasma membrane, and the majority of secreted proteins, contain oligosaccharide residues that are post-translationally added to the endoplasmic reticulum and in the Golgi apparatus (see p.230). By contrast, cytoplasmic proteins are rarely glycosylated. Glycoproteins can contain more than 50% carbohydrate however, the proportion of protein is generally much greater. 

The final steps of collagen post-translational modification, including assembly of colleen fibrils and collagen fibers, occur after the protein has been secreted from the cell. 

It is, however, well established that membrane glycoproteins and secreted proteins are glycosylated during the synthesis of their peptide backbone,12,1,-221 although post-translational glycosylation has also been reported.222-2233 The question arises as to whether these proteins... 

Many proteins synthesized in a cell are modified. For example, carbohydrates are often attached to the proteins found in cell membrane. Some proteins become phosphorylated. Such modifications either activate or inactivate the function of the protein. Therefore, a foreign gene should be properly manipulated to obtain a correct post-translational modification. For example, if an attachment of a carbohydrate to a protein is desired, one may design the process so as to secrete the protein out of a cell membrane. During this procedure the protein can be properly modified. However, such modification mechanisms can be different in each living organism. Therefore, careful selection of a proper cell line is necessary. 

SERCA pumps sequester Ca2+ in the ER lumen By maintaining appropriate Ca2+ concentrations in the ER lumen, SERCA pumps also play an essential role in protein synthesis, folding and transport of membrane and secreted proteins. This involves in particular chaperone-dependent processing and post-translational modifications which require a unique calcium rich environment. Chaperone molecules such as calreticulin and calnexin are involved in the quality control pathway in the ER (Berridge, 2002 Ellgaard and Helenius, 2003 Michalak et al., 2002). 

Ailor, E. and Betenbaugh, M. J. (1999) Modifying secretion and post-translational processing in insect cells. Curr. Opin. Biotechnol. 10, 142-145. 

Krasnoperov V, Bittner MA, Holz RW et al (1999) Structural requirements for a-latrotoxin binding and a-latrotoxin-stimulated secretion. A study with calcium-independent receptor of a-latrotoxin (CIRL) deletion mutants. J Biol Chem 274 3590-6 Krasnoperov V, Lu Y, Buryanovsky L et al (2002a) Post-translational proteolytic processing of the calcium-independent receptor of a-latrotoxin (CIRL), a natural chimera of the cell adhesion protein and the G protein-coupled receptor. Role of the G protein-coupled receptor proteolysis site (GPS) motif. J Biol Chem 277 46518-26... 

Mammalian cell culture is a technology used for the production of recombinant proteins of therapeutic use, as they can secrete proteins with post-translational modifications similar to those present in human proteins. The most important advantages of this capacity of the mammalian cell lines are that they secrete a protein with the similar characteristics to the original protein, so that the protein can be used for human treatment without generating immunological responses. 

Perez-Vilar J., Mabolo R. McVaugh C.T., Bertozzi C.R. and Boucher R.C. (2006). Mucin granule intraluminal organization in living mucous/goblet cells. Roles of protein post-translational modifications and secretion. J Biol Chem. 281, 4844-4855 Perez-Vilar J. (2007). Mucin granule intraluminal organization. Am J Respir Cell Mol Biol,... 

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